This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A distribution of content between a server and multiple receivers requires either to set up a point-to-point connection between the server and each receiver, or a multipoint connection. The point-to-point connection permits to distribute the content in a unicast means to each receiver, and provides a robust distribution. However with a significant number of receivers, it requires a heavy management of the connections. It may also dramatically increase the traffic over the network. The multicast distribution provides less network load, with a less robust distribution due to the absence of an acknowledgement mechanism. When multicast distribution is used, a solution must be found for repairing errors in the reception; for example, by means of retransmission demands. As an example of multicast delivery of content, IETF RFC 3926 defines the File Delivery over Unidirectional Transport protocol, noted FLUTE. The protocol defined in this standard is well adapted to answer the problems of scalability in terms of number of clients and heterogeneity in terms of bandwidth supported by the clients.
The standard DVB-H IP Data-casting standard, <<ETSI TS 102 472 V1.1.1 (2006 Jun.), Digital Video Broadcasting (DVB); IP Datacast over DVB-H; Content Delivery Protocols (CDP)>>, noted CDP standard hereinafter, defines a file repair mechanism. The file repair strategy adopted in the CDP standard is a one level file repair strategy and adopts the centralized client-server “File Repair” mode. It uses a file repair mechanism to assist the FLUTE protocol for achieving reliable file delivery other broadcast/multicast networks. Once it has detected the reception of an incomplete file, the FLUTE receiver launches a file repair mechanism. It consists in requesting the packets that are missing or corrupted. According to the FLUTE terminology, these packets are named symbol. The request is sent to a repair file server using a point-to-point connection. The request gathers basically the name of the file to be repaired and the list of missing symbols.
The FLUTE protocol defines a File Delivery Table, noted FDT, which comprises file description information of the files which have to be transmitted within a file delivery session. FLUTE protocol transmits the FDT from the content server in a multicast mode to all the clients. As this may be subject to transmission error, the reliability of the FDT file transmission can be enhanced with mechanisms such as a forward error correction or with retransmissions of the FDT during the session, that are well known per se. So at the end of the multicast content delivery each client knows exactly, the files which have to be transmitted in the session and the files which have been received. Each client may then indicate to the index server the files that are missing.
The mechanism specified in the CDP standard requires that the receiver receives at least a packet of the file. If no packet has been received, the receiver can not immediately and accurately detect that a file has not been received.